The present invention relates to oil pumps for internal combustion engines; more particularly, to a secondary oil pump for boosting oil pressure when the output pressure of the primary engine oil pump is low; and most particularly, to a secondary oil pump driven by a cam on the engine""s camshaft wherein pump-actuating cam lobes are out of phase with valve actuating cam lobes.
Oil pumps for internal combustion engines are well known. A primary engine oil pump may be, for example, a mechanically-driven positive-displacement gear pump fed from the engine""s crankcase and driven by rotation of the engine""s camshaft or crankshaft. Oil pump output flow is typically a direct function of the rotary speed of the engine. Because of engineered oil leaks between lubricated components in the oil pathway, and because of wear in those components during the lifetime of the engine, oil pressure also may be relatively low during periods of low engine speeds such as at idle and increases only as engine speed increases. Also, as engine temperature increases, oil viscosity decreases in known fashion, causing increased flow through the leaks and consequent reduced line pressure. In addition to insufficient engine lubrication, low oil pressure can result in slow or faulty actuation of oil-driven auxiliary engine devices, for example, camshaft phasers and variable valve actuators.
It is known to use an electrically-driven auxiliary pump to increase oil pressure for oil being supplied to a variable valve actuation mechanism.
What is needed is an inexpensive, reliable, mechanical means for maintaining a minimum oil pressure and flow in an internal combustion engine.
Another problem in an internal combustion engine is the amplitude of torque oscillation of the engine""s camshaft(s). During operation of the engine, while each valve is closed, the follower for the associated cam rides on the base circle portion of the cam. To open the valve, the follower rides up the front side of the eccentric lobe. The resistance caused by the opposing force of the valve return spring places a torque on the camshaft in a direction counter to the rotational direction of the camshaft. After the peak of the lobe is passed and the valve is closing, the direction of torque is reversed as the follower rides down the back side of the lobe, urged by the force of the valve spring. The camshaft is thus subjected to relatively violent torque reversals for each engine valve actuation resulting in oil pressure fluctuation (especially within the camshaft phaser), undesirable vibration, wear, and energy loss in the form of heat.
What is needed is a means for reducing the amplitude of torque oscillation of an engine camshaft.
It is a principal object of the present invention to reduce the amplitude of torque oscillation of an engine camshaft.
Briefly described, a secondary oil supply pump augments oil flow from a primary supply pump in an internal combustion engine. The secondary pump is a peristaltic piston pump driven by a dedicated cam disposed on a camshaft of the engine. Preferably, the pump cam is formed having a plurality of lobes equal in number to the number of valves actuated by the camshaft, and further, that each pump cam lobe is disposed at 180xc2x0 from a valve cam lobe such that the torque exerted by the closing valve assists in providing a pumping pulse to the secondary oil pump; and the torque exerted by termination of the pumping pulse assists in opening the next valve. In this way, the net amplitude of the camshaft torque oscillation is substantially reduced. A three-way valve responsive to inline pressure and, preferably, an engine control module governs the flow of oil either around the secondary pump at acceptably high primary pump pressures or through the secondary pump when primary pressure is unacceptably low.